Non-polar semiconductor light emission devices

ABSTRACT

A light emitting device includes a silicon substrate having a (100) upper surface. The (100) upper surface has a recess, the recess being defined in part by (111) surfaces of the silicon substrate. The light emitting device includes a GaN crystal structure over one of the (111) surfaces which has a non-polar plane and a first surface along the non-polar plane. Light emission layers over the first surface have at least one quantum well comprising GaN.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a Continuation-in-Part (CIP) patentapplication of and claims priority to commonly assigned co-pending U.S.patent application Ser. No. 13/026,698 entitled “Semi-polarSemiconductor Light Emission Devices,” filed Feb. 14, 2011, thedisclosure of which is incorporated herein by reference.

BACKGROUND

This patent application is related to solid state light emittingdevices.

Solid-state light sources, such as light emitting diodes (LEDs) andlaser diodes, can offer significant advantages over incandescent orfluorescent lighting. Solid-state light sources are generally moreefficient and produce less heat than traditional incandescent orfluorescent lights. When LEDs or laser diodes are placed in arrays ofred, green and blue elements, they can act as a source for white lightor as a multi-colored display. Although solid-state lighting offerscertain advantages, conventional semiconductor structures and devicesused for solid-state lighting are relatively expensive. The high cost ofsolid-state light emitting devices is partially related to theirrelatively complex and time-consuming manufacturing process.

Referring to FIG. 1, a prior art LED structure 100 includes a substrate105, such as sapphire. A buffer layer 110 is formed on the substrate105. The buffer layer 110 serves primarily as a wetting layer to promotesmooth, uniform coverage of the sapphire substrate. The buffer layer 110is typically deposited as a thin amorphous layer using Metal OrganicChemical Vapor Deposition (MOCVD). An n-doped Group III-V compound layer120 is formed on the buffer layer 110. The n-doped Group III-V compoundlayer 120 is typically made of GaN. An InGaN quantum-well layer 130 isformed on the n-doped Group III-V compound layer 120. An active GroupIII-V compound layer 140 is then formed on the InGaN quantum-well layer130. A p-doped Group III-V compound layer 150 is formed on the layer140. A p electrode 160 (anode) is formed on the p-doped Group III-Vcompound layer 150. An n-electrode 170 (cathode) is formed on then-doped Group III-V compound layer 120.

The GaN crystal has different electric properties along differentcrystal directions. The (0001) crystal planes are perpendicular to thec-axis and have the highest electric polarity compared to other planes.The (1-100) crystal planes are perpendicular to the m axis and arenon-polar. Other GaN crystal planes such as (1-101) are semi-polar andhave electric polarity less than that of the (0001) crystal planes.

Different crystal planes of GaN crystal also have different opticalproperties. The internal quantum efficiency (IQE) is the highest for thenon-polar (1-100) crystal planes and is lower for the semi-polar crystalplanes, such as (0001) plane. The polar (0001) crystal planes have thelowest quantum efficiency. In a light emitting device, it is desirableto produce light emission from the non-polar or semi-polar crystalplanes to obtain high emission intensity.

Early GaN LEDs had been formed on sapphire, silicon carbide, or spinelsubstrates (105 in FIG. 1). Recently, attempts have been made to growGaN light emitting devices having non-polar emission surfaces on LiAlO₂substrates. Although it was found that the light emission of these LEDstructures were spectrally stable and polarized, the emissionintensities were low due to numerous defects formed in the GaN crystalsduring growth on the LiAlO₂ substrate.

SUMMARY

This patent application discloses light emitting devices that haveimproved light emission efficiency and light emission intensity,compared to prior art GaN LEDs, by using both non-polar and semi-polarGaN crystal surfaces as the base for quantum wells. The light emissionfrom the disclosed light emitting devices is highly polarized, which isvery useful for many display applications.

The disclosed devices may have certain advantages, including improveddevice reliability and lifetime, as they employ single GaN crystals withvery low defect density. They can be tailored in different form factorsto suit different applications; and they can be fabricated on a siliconsubstrate, which is compatible with many microelectronic devices.

In one general aspect, the present invention relates to a light emittingdevice that includes a silicon substrate having a (111) surface, a GaNcrystal structure over the (111) surface of the silicon substrate, theGaN crystal structure having a non-polar plane, a first surface parallelto the non-polar plane, and light emission layers over the firstsurface. The light emission layers include at least one quantum wellcomprising GaN.

In another general aspect, these light emitting devices can include asilicon substrate having a (100) upper surface, the (100) upper surfacehaving a recess, the recess being defined in part by a (111) surface ofthe silicon substrate; a GaN crystal structure over the (111) surface,the GaN crystal structure having a non-polar plane; a first surfaceparallel to the non-polar plane; and light emission layers over thefirst surface, the light emission layers having at least one quantumwell comprising GaN.

Implementations of these light emitting devices may include one or moreof the following. The first surface can be substantially perpendicularto the (111) surface of the silicon substrate. The first surface can bebordered with an edge of the (111) surface of the silicon substrate. Thefirst surface can be substantially perpendicular to the m-axis in the(1-100) direction of the GaN crystal structure. The GaN crystalstructure can include a semi-polar plane and a second surface parallelto the semi-polar plane. The GaN crystal structure can include a polarplane and a third surface parallel to the polar plane. The GaN crystalstructure can include a semi-polar plane and a second surface parallelto the non-polar plane, wherein the GaN crystal structure can include apolar plane and a third surface parallel to the polar plane, wherein thesecond surface is positioned between the first surface and the thirdsurface. The first surface and the second surface can intercept eachother at an angle between about 142° and about 162°. The second surfaceand the third surface can intercept each other at an angle between about108° and about 128°. The GaN crystal structure can be doped so as to beelectrically conductive, wherein the light emitting device can furtherinclude an upper electrode layer on the light emission layers, whereinthe light emission layers can emit light when an electric field isapplied across the light emission layers between the GaN crystalstructure and the upper electrode layer. The light emitting device canfurther include a reflective layer between the (111) surface of thesilicon substrate and the GaN crystal structure. The light emittingdevice can further include a buffer layer between the reflective layerand the (111) surface of the silicon substrate. The silicon substratecan further include a (100) upper surface; and a recess, in part definedby the (111) surface of the silicon substrate, formed in the (100) uppersurface. The recess can have the shape of a trench, an inverse pyramid,or a truncated inverse pyramid. The quantum well can include InGaN andGaN layers.

In one general aspect, the present invention relates to a light emittingdevice that can include a silicon substrate comprising a (111) surfaceand a GaN crystal structure over the (111) surface, wherein the GaNcrystal structure can have a first surface parallel to a semi-polarplane of the GaN crystal structure, and a second surface parallel to apolar plane of the GaN crystal structure. Light emission layers that canhave at least one quantum well of InGaN/GaN or AlGaN/GaN lie over thefirst surface of the GaN crystal structure.

In another general aspect, these light emitting devices can include asilicon substrate having a (100) silicon upper surface with a recess inpart defined by (111) silicon surfaces. A GaN crystal structure liesover one of the (111) silicon surfaces, and has a first surface parallelto a semi-polar plane of the GaN crystal structure, and a second surfacealong a polar plane of the GaN crystal structure. The light emissionlayers have at least one quantum well comprising InGaN that lies overthe first surface of the GaN crystal structure.

Implementations of the light emitting devices may include one or more ofthe following. The first surface can form an angle between about 52° andabout 72° relative to the m-axis of the GaN crystal structure. The firstsurface can be substantially parallel to the (1-101) GaN crystal plane.The first surface can intercept the (111) surface of the siliconsubstrate at an angle between about 52° and about 72°. The secondsurface can be substantially parallel to the (0001) GaN crystal planeand perpendicular to the c-axis of the GaN crystal structure. The firstsurface and the second surface can intercept each other at an anglebetween about 108° and about 128°.

The GaN crystal structure can be doped and can perform as a lowerelectrode layer for the light emission layers. The light emitting devicecan further include an upper electrode layer on the light emissionlayers, wherein the light emission layers can emit light when anelectric field is applied across the light emission layers between theGaN crystal structure and the upper electrode layer. The GaN crystalstructure can be doped with an element to provide n-type electricalcharacteristics, with one example being silicon. The light emittingdevice can further include a reflective layer between the (111) surfaceof the silicon substrate and the GaN crystal structure. The reflectivelayer can include silicon doped AlGaN or silicon doped AN. The lightemitting device can further include a buffer layer between thereflective layer and the (111) surface of the silicon substrate. Thebuffer layer can include silicon doped AN. The silicon substrate canfurther include a (100) surface and a recess formed in its (100) uppersurface, the recess defined in part by the (111) surface. The recess canhave the shape of an elongated trench, an inverse pyramid or a truncatedinverse pyramid. The quantum well can be formed by InGaN and GaN, orAlGaN and GaN, as examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings, which are incorporated in and form a part of thespecification, illustrate embodiments of the present invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a cross-sectional view of a prior art LED structure.

FIG. 2 is a cross-sectional view of a GaN light emitting device inaccordance with an embodiment of the present invention.

FIG. 3A is a schematic representation of a cross-section of multi-layerstructure of the light emitting device shown in FIG. 2.

FIG. 3B illustrates material compositions and formation conditions fordifferent layers of the light emitting device shown in FIGS. 2 and 3A.

FIGS. 4A and 4B are detailed cross-sectional views illustrating thegrowth of GaN crystal on the Si (111) surface shown in FIG. 2.

FIG. 5A is a perspective cross-sectional view of the light emittingdevice shown in FIGS. 2, 3A and 4B.

FIG. 5B is a perspective view of the light emitting device shown in FIG.5A.

FIG. 6A illustrates the light emission directions from the semi-polarand the polar GaN crystal surfaces.

FIG. 6B is a photograph of the light emitting device of FIGS. 2, 3A and5A during light emission.

FIG. 7 is a perspective view of an array of light emitting devicessimilar to the ones shown in FIGS. 5A and 5B, formed on a commonsubstrate.

FIG. 8 is a perspective view of a light emitting device having adifferent form factor from the light emitting device shown in FIG. 7.

FIG. 9 is a perspective view of an array of light emitting devicessimilar to the one shown in FIG. 8, formed on a common substrate.

FIGS. 10A-10C are detailed cross-sectional views illustrating the growthof GaN crystal in accordance with an embodiment of the presentinvention.

FIG. 11 is a cross-sectional view of a GaN light emitting device inaccordance with another embodiment of the present invention.

FIG. 12A is a perspective cross-sectional view of the light emittingdevice shown in FIG. 11.

FIG. 12B is a perspective view of the light emitting device shown inFIGS. 11 and 12A.

FIG. 13 is a perspective view of an array of light emitting devicessimilar to the ones shown in FIGS. 11, 12A and 12B, formed on a commonsubstrate.

FIG. 14 is a perspective view of a light emitting device having adifferent form factor from the light emitting device shown in FIGS. 11,12A and 12B.

FIG. 15 is a perspective view of an array of light emitting devicessimilar to the one shown in FIG. 14, formed on a common substrate.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

Referring to FIG. 2, a light emitting device 200 includes a siliconsubstrate 210 having a (100) upper surface 201, a recess 220 defined atleast in part by (111) surfaces 202, buffer and reflective layers 230 onthe surfaces 202, a doped GaN crystal structure 240 on the buffer andreflective layers 230, light emission layers comprising quantum welllayers 250 on the doped GaN crystal structure 240, and a doped GaN layer260 on the quantum well layers 250. The doped GaN crystal structure 240and the doped GaN layer 260 are conductive and can respectively serve aslower and upper electrodes for the quantum well layers 250. An electrodelayer 205 is formed on the upper surface 201 and is in electricconnection with the doped GaN layer 260.

A recess 220 in the light emitting device 200 is formed in the (100)upper surface 201 of the silicon substrate 210. A SiN mask (not shown)formed on the (100) upper surface can have square or rectangle openings.The dimensions of these openings can be in the range from tens ofmicrons to a few millimeters. The openings can be formed using etchingmethods known in the art, and described in co-pending U.S. patentapplication Ser. No. 12/177,114 by Shaoher Pan, filed on Jul. 21, 2008,and entitled “Light Emission Device,” the disclosure of which isincorporated by reference herein. Etching through openings in the SiNmask results in the formation of recess 220 having the (111) surfaces202. The (111) surfaces 202 are tilted at a 54.7° angle relative to the(100) surfaces (the upper surface 201) of the silicon substrate 210.

The buffer and reflective layers 230, shown diagrammatically in FIG. 2,are shown in FIG. 3A. Referring now to FIG. 3A, these layers include abuffer layer 231, a second buffer layer 232, and a reflective layer 235.Referring to FIGS. 3A and 3B, the buffer layer 231, also called ahigh-temperature buffer layer, comprises silicon doped AlN. The 30 nmthick, high temperature silicon doped AlN buffer layer 231 is depositedon the (111) surface 202 of the substrate 210 (shown in FIG. 2) at atemperature between about 1120° C. and 1170° C., and a pressure of about25 mbar for about 15 minutes. During this procedure, the (100) surface(the upper surface 201) is masked by mask layer so the AlN buffer layer231 is deposited only on the (111) surface 202 of the substrate 210 andnot in the area beneath electrode 205. The second 10 nm thick bufferlayer 232, also called the low-temperature buffer layer, also comprisessilicon doped AlN. The second buffer layer 232 is deposited on thebuffer layer 231 at a lower temperature of about 755° C., at a pressureof about 50 mbar for about 5 minutes. The 400 nm thick reflective layer235, formed by AlGaN doped with silicon is deposited on the buffer layer232 at a temperature from about 1220° C. to 1030° C. and at a pressureof about 25 mbar for about 15 minutes.

A layer of doped GaN crystal structure 240 more than 1 μm thick isdeposited on the reflective layer 235 at about 970° C. and at a pressureof about 250 mbar for more than 1 hour. The doped GaN crystal structure240 comprises GaN doped by silicon. Referring now both to FIGS. 2 and3B, during deposition, the doped GaN crystal structure 240 grows along ac-axis (i.e., the (0001) direction), which forms a surface 242 that issubstantially parallel to the (0001) crystal plane and perpendicular tothe c-axis. The surface 242 is also substantially parallel to the (111)surface 202 of the substrate 210. The surface 242 of the doped GaNcrystal structure 240 is an electrically polar surface. The doped GaNcrystal structure 240 has an m-axis along the (1-100) direction, whichdefines electrically non-polar planes. The m-axis or the (1-100)direction is substantially parallel to the (111) surface 202 of thesubstrate 210.

The doped GaN crystal structure 240 also grows naturally in the (1-101)direction, which defines a surface 241 that is parallel to the (1-101)crystal plane. The surface 241 is at an angle between about 52° andabout 72° or, for example, approximately 62°, relative to m-axis of thedoped GaN crystal structure 240. The surface 241 is at the same anglerelative to the (111) surface 202 of the substrate 210. The (1-100)direction and the (1-101) direction are offset by approximately thatsame angle. The surface 241 is semi-polar and has an electric polaritylower than that of the surface 242. The surface 241 and the surface 242intercept at an angle between about 108° and about 128°, or for example,118°. The doped GaN crystal structure 240 also includes surfaces 245formed in the deep central portion of the recess 220. The orientationsof the surfaces 245 are in part determined by the deposition materialsof the quantum well layers 250 used in the deep central region of therecess 220.

The quantum well layers 250 comprise a plurality (for example eight)repetitive, interleaved GaN and InGaN layers, each with a thickness of20 nm and 3 nm, respectively. The quantum well layers 250 are formed atabout 740° C. and at a pressure of about 200 mbar. The buffer layers 231and 232 (FIG. 3A) can reduce mechanical strain between the (111) siliconsurfaces 202 and the doped GaN crystal structure 240 to allow the dopedGaN crystal structure 240 to be epitaxially grown on the (111) surfaces202 of the silicon substrate 210. The buffer layers 231 and 232 can alsoprevent cracking and delamination in the quantum well layers 250, whichimproves light emitting efficiency of the light emitting device 200. The50 nm thick GaN layer 260 (the upper electrode layer), doped for examplewith Mg, is next deposited on the quantum well layers 250 at 870° C. andat a pressure of 200 mbar for about 4 min (FIG. 3B).

The buffer layers 231 and 232, the reflective layer 235, and the quantumwell layers 250 can be formed using atomic layer deposition (ALD), MetalOrganic Chemical Vapor Deposition (MOCVD), Plasma Enhanced ChemicalVapor Deposition (PECVD), Chemical Vapor Deposition (CVD), or Physicalvapor deposition (PVD). The doped GaN crystal structure 240 and thedoped GaN layer 260 can be deposited by PVD, PECVD, or CVD.

In light emitting operation, an electric voltage is applied across thelower and the upper electrodes that include, respectively, the doped GaNcrystal structure 240 and the doped GaN layer 260. The electric currentpassing through the quantum well layers 250 can cause electrons andholes to recombine, resulting in light emission.

The growth of the doped GaN crystal structure 240 is illustrated indetail in FIGS. 4A and 4B. The GaN crystal structure 240 is initiallydefined by semi-polar surfaces 241 and 243. The m-axis (the (1-100)direction) that defines the non-polar planes is substantially parallelto the surface 202 of the silicon substrate. During the GaN crystalgrowth, the electrically polar surface 242 (shown in FIG. 4B) parallelto the m-axis is formed at the growth front. The surface 241 is at anangle of approximately 62° relative to the (111) surface 202 of thesilicon substrate. The GaN growth rate is higher along the c-axis (i.e.,in the (0001) direction) than along the m-axis (the (1-100) direction).The GaN growth rate is in turn higher along the m-axis (the (1-100)direction) than along the (1-101) direction.

Details of the light emitting device 200 are shown in perspective viewsin FIGS. 5A and 5B. Referring to FIGS. 2, 5B, 6A, and 6B, the recess 220has the shape of an inverse pyramid. FIG. 6A illustrates the lightemission directions from a semi-polar surface 241 and a polar GaNcrystal surface 242. FIG. 6B is a photograph of a light emitting deviceas described above during light emission. The center of the lightemitting device is partially blocked by the tip of an electrode that ispressed in contact with the upper electrode to provide the voltageacross the quantum well layers. The light emissions from the quantumwell layers on the semi-polar surfaces (241) are much stronger thanthose from the quantum well layers on the polar surfaces (242), and thelight emissions from quantum well layers in the direction of thenon-polar plane, shown by the arrow in FIG. 2, are the strongest of all.It should be noted that in the disclosed light emitting device, therecess and the growth of the GaN structure are arranged such as to allowthe semi-polar surface 241 of the GaN structure to be exposed to theoutside in the direction of primary light emission in order to maximizethe light emission from the stronger light emission surfaces.Accordingly, a significant advantage of the disclosed light emittingdevice is to provide much increased light emission intensity by forminglight emission layers on semi-polar surfaces of a doped GaN structure.

An array of light emitting devices 200A-200D can be formed on a commonsubstrate 210, as shown in FIG. 7. Each of these light emitting devices200A-200D has a similar structure to the one shown in FIGS. 2-5B. Thearray can have different numbers of light emitting structures, as shownin FIGS. 2-5B, to suit the needs of different lighting and displayapplications, for example, 2×1, 2×2, 3×2, 3×3, 4×4, etc.

The light emitting devices can be made in different shapes and formfactors. The recesses in the silicon substrate can have the shapes of aninverse pyramid or a truncated inverse pyramid to provide asubstantially square light emitting device. The recesses in the siliconsubstrate can have the shape of an elongated trench to provide a linearshaped light emitting device. A light emitting device 800, shown in FIG.8, can have a linear shaped light emission area out of the upperelectrode layer 260. An elongated trench is first formed in thesubstrate 210, followed by the formations of the buffer layers, thereflective layer, the doped GaN structure, the quantum well layers andthe upper electrode layer, using the same steps as described above inrelation to the light emitting devices 200A-200D. Furthermore, aplurality of linear shaped light emitting devices 800A-800D can beformed on a common substrate 210, as shown in FIG. 9.

In some embodiments, a non-polar plane can be grown in a GaN structureusing the edge of the substrate as a stopping point. Referring to FIG.10A, 10B and 10C, the GaN crystal structure 240 is initially defined bythe semi-polar surfaces 241 and 243. The m-axis (in the (1-100)direction) that defines the non-polar plane is substantially parallel tothe surface 202 of the silicon substrate 210. During the growth of theGaN structure 240, the electrically polar surface 242 parallel to them-axis is formed at the growth front. The semi-polar surface 241 is atan angle of approximately 62° relative to the (111) surface 202 of thesilicon substrate. The GaN growth rate is higher along the c-axis (i.e.,in the (0001) direction) than along the m-axis (the (1-100) direction).

Referring now to FIG. 10C, as the GaN structure 240 grows, such that thesurface 243 reaches an edge 215 of the silicon substrate 210, the GaNcrystal growth is inhibited at the edge 215, while the additionalcrystal material continues to grow on the surface 243. A new non-polarsurface 244 appears between the edge 215 and the semi-polar surface 243.The new surface 244 is perpendicular to the m-axis (i.e., the (1-100)crystal axis) and is bordered with the edge 215. The direction of growthis parallel to m-axis. The new surface 244 is substantiallyperpendicular to the m-axis of the GaN crystal. The new surface 244 isalso substantially perpendicular to the (111) surface 202 of the siliconsubstrate 210, and is at an approximately 125° angle relative to the(100) crystal plane in the silicon substrate 210. In FIG. 11 the uppersurface 201 is in the (100) plane. The sloped surface in the trench isin the (111) plane. The (111) plane is oriented horizontally in FIGS.10A-10C for easy viewing.

It should be noted that the non-polar surface does not naturally appearin the growth front in an uninhibited crystal growth environment,because the GaN growth rate is greater along the m-axis (the (1-100)direction) than along the (1-101) direction. The formation of thenon-polar surface is achieved in the present invention by first forminga GaN crystal structure near the edge of the surface of a (111) siliconsubstrate and continuing to grow the GaN crystal structure until thenon-polar surfaces and the semi-polar surfaces grow to the desireddimensions.

Using the above described technique, an improved light emitting device900 can be constructed as shown in FIG. 11. The light emitting device900 includes a silicon substrate 210 having a (100) upper surface 201, arecess 220 defined at least in part by (111) surfaces 202, buffer andreflective layers 230 on the surfaces 202, a doped GaN crystal structure240 on the buffer and reflective layers 230, light emission layerscomprising quantum well layers 250 on the doped GaN crystal structure240, and a doped GaN layer 260 on the quantum well layers 250. The dopedGaN crystal structure 240 and the doped GaN layer 260 are conductive andcan respectively serve as lower and upper electrodes for the quantumwell layers 250. An electrode layer 205 formed on the upper surface 201is in electric connection with the doped GaN layer 260.

A recess 220 in the light emitting device 200 is formed in the (100)upper surface 201 of the silicon substrate 210. A SiN mask (not shown)formed on the (100) upper surface can have square or rectangle openings.The dimensions of these openings can be in the range from tens ofmicrons to a few millimeters, which can be formed using etching methodsknown in the art, and described in co-pending U.S. patent applicationSer. No. 12/177,114 by Shaoher Pan, filed on Jul. 21, 2008, and entitled“Light Emission Device,” the disclosure of which is incorporated byreference herein. Etching through openings in the SiN mask results inthe formation of recess 220 having the (111) surfaces 202. The (111)surfaces 202 are tilted at a 54.7° angle relative to the (100) surfaces(the upper surface 201) of the silicon substrate 210. Details about thestructure and formation process of the buffer and reflective layers 230are discussed above in relation to FIG. 3A.

A layer of doped GaN crystal structure 240 more than 1 μm thick isdeposited on the reflective layer 235 at about 970° C. and at a pressureof about 250 mbar for more than 1 hour. The doped GaN crystal structure240 comprises GaN doped by silicon. Referring now both to FIGS. 10C and9, during deposition, the doped GaN crystal structure 240 grows along ac-axis (i.e., the (0001) direction), which forms a surface 242 that issubstantially parallel to the (0001) crystal plane and perpendicular tothe c-axis. The surface 242 is also substantially parallel to the (111)surface 202 of the substrate 210. The surface 242 of the doped GaNcrystal structure 240 is an electrically polar surface. The doped GaNcrystal structure 240 has an m-axis along the (1-100) direction, whichdefines electrically non-polar planes. The m-axis or the (1-100)direction is substantially parallel to the (111) surface 202 of thesubstrate 210.

The doped GaN crystal structure 240 also grows naturally in the (1-101)direction, which defines a surface 241 that is parallel to the (1-101)crystal plane. The surface 241 is semi-polar and has an electricpolarity lower than that of the surface 242. The surface 241 and thesurface 242 intercept at an angle between about 108° and about 128°, orfor example, 118°. Referring to FIG. 5A, the doped GaN crystal structure240 also includes surfaces 245 formed in the deep central portion of therecess 220. The orientations of the surfaces 245 are in part determinedby the deposition materials of the quantum well layers 250 used in thedeep central region of the recess 220.

Referring to FIG. 10C, as the surface 241 grows to the edge 215 of the(111) surface 202 of the substrate 210, the crystal growth of thesemi-polar surface is inhibited, as described above. As the GaNstructure 240 grows, a non-polar surface 244 appears between the edge215 and the semi-polar surface 241 despite the higher crystal growthrate on the non-polar surface 244 in comparison to the semi-polarsurface 241. The non-polar surface 244 has substantially no electricpolarity and GaN crystal thus grows along and is perpendicular to them-axis (1-100). As shown in FIG. 11, the surface 241 and the surface 244intercept at an angle between about 142° and about 162° or, for example,approximately 152°. The surface 244 is at about the right angle relativeto the (111) surface 202 of the substrate 210.

Next, quantum well layers 250 comprise a plurality (for example eight)repetitive, interleaved GaN and InGaN layers, each with a thickness of20 nm and 3 nm, respectively. As shown in details in FIGS. 3A and 3B,the quantum well layers 250 can be formed at about 740° C. and at apressure of about 200 mbar. The 50 nm thick GaN layer 260 (the upperelectrode layer), doped for example with Mg, is next deposited on thequantum well layers 250 at 870° C. and at a pressure of 200 mbar forabout 4 min.

Referring again to FIG. 11, in light emitting operation, an electricvoltage is applied across the lower and the upper electrodes thatinclude, respectively, the doped GaN crystal structure 240 and the dopedGaN layer 260. The electric current passing through the quantum welllayers 250 can cause electrons and holes to recombine, resulting inlight emission.

The light emitting device 900 is shown in perspective views in FIGS. 12Aand 12B. The doped GaN layer 260 on the quantum well layers 250 includesa light emission surface 261 over the semi-polar surface 241, a lightemission surface 262 over the polar surface 242, and a light emissionsurface 264 over the non-polar surface 244. The light emissions from thequantum well layers 250 on the semi-polar surfaces 241 are stronger thanthose from the quantum well layers 250 on the polar surfaces 242. Thelight emissions from quantum well layers 250 on the non-polar surface244 are the strongest of all. Moreover, the surfaces 264 and 261respectively over the non-polar and semi-polar surfaces 244, 241 arefacing upward in FIGS. 12A, 12B, that is, along the primary illuminatingdirection.

It should be noted that in the disclosed light emitting device, therecess and the growth of the GaN structure are arranged such as to allowthe non-polar surfaces and the semi-polar surfaces of the GaN structureto be exposed to the outside in order to maximize the light emissionfrom the stronger light emission surfaces. Accordingly, a significantadvantage of the disclosed light emitting device is to provide muchincreased light emission intensity by forming light emission layers onthe non-polar and semi-polar surfaces of a doped GaN structure in theprimary light emission directions.

Referring to FIG. 13, an array 1300 of light emitting devices 900A-900Dhaving the structure of the light emitting device 900 (shown in FIG.12B) can be formed on a common substrate 210. The array 1300 can havedifferent numbers of light emitting structures to suit the needs ofdifferent lighting and display applications, for example, 2×1, 2×2, 3×2,3×3, 4×4, etc.

The light emitting devices can be made in different shapes and formfactors. The recesses in the silicon substrate can have the shapes of aninverse pyramid or a truncated inverse pyramid to provide asubstantially square light emitting device. The recesses in the siliconsubstrate can have the shape of an elongated trench having structures asshown in the cross-sectional view in FIG. 11, to provide a linear shapedlight emitting device. A light emitting device 1400, shown in FIG. 14,can have a linear shaped light emission area out of the surfaces 261,262, and 264. An elongated trench is first formed in the substrate 210,followed by the formations of the buffer layers, the reflective layer,the doped GaN structure, the quantum well layers, and the upperelectrode layer, using the same steps as described above in relation tothe light emitting devices 900, 900A-900D shown in FIG. 13. Furthermore,a plurality of linear shaped light emitting devices 1400A-1400D can beformed on a common substrate 210, as shown in FIG. 15.

The presently disclosed light emitting devices can have one or more ofthe following advantages. First, light emission efficiency and lightemission intensity can be significantly increased in comparison withconventional GaN LED devices by using non-polar and semi-polar GaNcrystal surfaces as a base for the quantum wells. The light emissionfrom the disclosed light emitting device is also highly polarized, whichis very useful for many display applications. Another advantage of thepresent light emitting device is to reduce defect density in the GaNcrystals, which improves device reliability and lifetime. Additionally,the disclosed light emitting devices can be tailored in different formfactors to suit different applications. Furthermore, the disclosed lightemitting devices can be fabricated on a silicon substrate, which is morecompatible with the fabrication of many microelectronic devices.

The foregoing description and drawings should be considered asillustrative only of the principles of the invention. The describeddevices may be configured in a variety of shapes and sizes and the scopeof the invention is not limited by the dimensions of the preferredembodiments. Numerous applications of the present invention will readilyoccur to those skilled in the art. Therefore, the invention is notintended to be limited to the specific examples disclosed or the exactconstruction, operation or dimensions shown and described. Rather, allsuitable modifications and equivalents fall within the scope of theinvention. For example, one of the GaN crystal structure and the dopedGaN layer can be n-doped and the other p-doped. The types of doping inthe two components can be switched while still compatible with thepresently disclosed light emitting device. The disclosed LED structuremay be suitable for emitting green, blue, and other colored lights.Moreover, the recesses can have other shapes than the examples describedabove. For example, the openings in the mask on the upper surface mayhave shapes different from squares or rectangles. In another example, a(111) silicon wafer can be used as a substrate to allow trenches having(100) surfaces to form in the substrate.

1. A light emitting device, comprising: a silicon substrate having a(111) surface; a GaN crystal structure over the (111) surface of thesilicon substrate, the GaN crystal structure having a non-polar planeand a first surface parallel to the non-polar plane; and light emissionlayers over the first surface, the light emission layers having at leastone quantum well comprising GaN.
 2. The light emitting device of claim1, wherein the first surface is substantially perpendicular to the (111)surface of the silicon substrate.
 3. The light emitting device of claim1, wherein the first surface is bordered with an edge of the (111)surface of the silicon substrate.
 4. The light emitting device of claim1, wherein the first surface is substantially perpendicular to them-axis in the (1-100) direction of the GaN crystal structure.
 5. Thelight emitting device of claim 1, wherein the GaN crystal structurecomprises a semi-polar plane and a second surface parallel to thesemi-polar plane.
 6. The light emitting device of claim 5, wherein theGaN crystal structure comprises a polar plane and a third surfaceparallel to the polar plane.
 7. The light emitting device of claim 6,wherein the second surface is positioned between the first surface andthe third surface.
 8. The light emitting device of claim 7, wherein thefirst surface and the second surface intercept each other at an anglebetween about 142 degrees and about 162 degrees.
 9. The light emittingdevice of claim 7, wherein the second surface and the third surfaceintercept each other at an angle between about 108 degrees and about 128degrees.
 10. The light emitting device of claim 1, wherein the GaNcrystal structure is doped and is electrically conductive, the lightemitting device further comprising: an upper electrode layer on thelight emission layers, wherein the light emission layers are configuredto emit light when an electric field is applied across the lightemission layers between the GaN crystal structure and the upperelectrode layer.
 11. The light emitting device of claim 1, furthercomprising a reflective layer between the (111) surface of the siliconsubstrate and the GaN crystal structure.
 12. The light emitting deviceof claim 11, further comprising a buffer layer between the reflectivelayer and the (111) surface of the silicon substrate.
 13. The lightemitting device of claim 1, wherein the silicon substrate furthercomprises: a (100) upper surface; and a recess, in part defined by the(111) surface of the silicon substrate, formed in the (100) uppersurface.
 14. The light emitting device of claim 13, wherein the recesshas the shape of a trench, an inverse pyramid, or a truncated inversepyramid.
 15. The light emitting device of claim 1, wherein the quantumwell comprises InGaN and GaN layers.
 16. A light emitting device,comprising: a silicon substrate having a (100) upper surface, the (100)upper surface having a recess, the recess being defined in part by (111)surfaces of the silicon substrate; a GaN crystal structure over one ofthe (111) surfaces, the GaN crystal structure having a non-polar planeand a first surface parallel to the non-polar plane; and light emissionlayers over the first surface, the light emission layers having at leastone quantum well comprising GaN.
 17. The light emitting device of claim16, wherein the recess has the shape of a trench, an inverse pyramid, ora truncated inverse pyramid.
 18. The light emitting device of claim 16,wherein the first surface is substantially perpendicular to the (111)surface of the silicon substrate.
 19. The light emitting device of claim16, wherein the first surface is bordered with an edge of the (111)surface of the silicon substrate.
 20. The light emitting device of claim16, wherein the GaN crystal structure comprises a semi-polar plane and asecond surface parallel to the semi-polar plane, wherein the GaN crystalstructure comprises a polar plane and a third surface parallel to thepolar plane, wherein the second surface is positioned between the firstsurface and the third surface.
 21. The light emitting device of claim20, wherein the first surface and the second surface intercept eachother at an angle between about 142 degrees and about 162 degrees. 22.The light emitting device of claim 20, wherein the second surface andthe third surface intercept each other at an angle between about 108degrees and about 128 degrees.
 23. The light emitting device of claim16, wherein the GaN crystal structure is doped and is electricallyconductive, the light emitting device further comprising: an upperelectrode layer on the light emission layers, wherein the light emissionlayers are configured to emit light when an electric field is appliedacross the light emission layers between the GaN crystal structure andthe upper electrode layer.
 24. The light emitting device of claim 16,further comprising a reflective layer between the GaN crystal structureand one of the (111) surfaces of the silicon substrate.
 25. The lightemitting device of claim 24, further comprising a buffer layer betweenthe reflective layer and the one of the (111) surfaces of the siliconsubstrate.